Papitto, Alessandro;
Di Marco, Alessandro;
Poutanen, Juri;
Salmi, Tuomo;
Illiano, Giulia;
La Monaca, Fabio;
Ambrosino, Filippo;
... Zane, Silvia; + view all
(2025)
Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2–604207.
Astronomy & Astrophysics
, 694
, Article A37. 10.1051/0004-6361/202451775.
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Abstract
We report the discovery of polarized X-ray emission from an accreting millisecond pulsar. During a 10-day-long coverage of the February 2024 outburst of SRGA J144459.2−604207, the Imaging X-ray Polarimetry Explorer (IXPE) detected an average polarization degree of the 2–8 keV emission of 2.3% ± 0.4% at an angle of 59◦ ± 6◦ (east of north; the uncertainties quoted are at the 1σ confidence level). The polarized signal shows a significant energy dependence with a degree of 4.0% ± 0.5% between 3 and 6 keV and <1.5% (90% c.l.) in the 2–3 keV range. We used NICER, XMM–Newton, and NuSTAR observations to obtain an accurate pulse-timing solution and to perform a phase-resolved polarimetric analysis of IXPE data. We did not detect any significant variability in the Stokes parameters Q and U with the spin and orbital phases. We used the relativistic rotating-vector model to show that a moderately fan-beam emission from two point-like spots at low magnetic obliquity ('10◦) is compatible with the observed pulse profile and polarization properties. IXPE also detected 52 type I X-ray bursts whose recurrence time ∆trec increased from 2 to 8 h as a function of the observed count rate C as ∆trec ∝ C−0.8. We stacked the emission observed during all the bursts and obtained an upper limit on the polarization degree of 8.5% (90% c.l.).
| Type: | Article |
|---|---|
| Title: | Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2–604207 |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1051/0004-6361/202451775 |
| Publisher version: | https://doi.org/10.1051/0004-6361/202451775 |
| Language: | English |
| Additional information: | Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | magnetic fields / polarization / methods: observational / stars: neutron / pulsars: individual: SRGA J144459.2–604207 / X-rays: binaries |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10205282 |
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